1. Field of the Invention
The present invention relates to a picture signal generator, and more specifically to an apparatus for generating a picture signal for producing a different picture to be superimposed with a broadcast image in a screen of a scan type display such as a cathode ray tube. More particularly, the present invention relates to a circuit for precisely defining a horizontal indication start position of the above mentioned different picture.
2. Description of Related Art
In the prior art, in the case of indicating a different picture to be superimposed with a broadcast image in a screen of a scan type display such as a cathode ray tube, a horizontal indication start position signal for the different picture has been generated by counting, from a trail edge of a horizontal synchronism signal, the number of pulses which are generated in synchronism with the horizontal synchronism signal but at a repetition frequency sufficiently higher than that of the horizontal synchronism signal. However, this method has been disadvantageous in that when the pulse width or duration of the horizontal synchronism signal varies, the timing of generation of the horizontal indication start position signal also varies, with the result that the different picture will shift in the horizontal direction.
In the prior art, therefore, an generator of the horizontal indication start position signal had to be adjusted while viewing the position of the superimposed different picture in the screen of the horizontal scan type display.